This proposal involves design of the major capabilities of a dynamical system software package, with initial "rapid prototyping" implementation in the MLAB environment. Such major capabilities include analyzing chaotic data and fit data to models, iterate dynamical systems and plot trajectories, defining top level functions and dynamically changing global system parameters, etc. During late Phase I and Phase II, we will adapt recent mathematical advances in chaotic systems research to improve the modeling and controlling of cardiac chaos. This involves programming more built-in functions and models to facilitate computing periodic points, stable and unstable manifolds of dynamical systems, etc. which are required in control of cardiac chaos and other chaotic biochemical dynamical systems. Finally, late Phase II, design of graphical user interfaces for the software to supply easy tool for input functions, initial conditions, adjust parameters and allow users to perform multiple operations in different windows at the same time. PROPOSED COMMERCIAL APPLICATION: The need to model chaotic dynamical systems interactively as the system parameters changes in the design, analysis, and control of realistic models for biological and technological processes. Thus, software to facilitate such interactive modeling capability will be widely applicable. It will be used to the extent that the software is easy to use and reasonably priced.